A plurality of electronic devices are equipped with a touch-sensitive screen, a so-called touch screen, instead of a keyboard. One of the most common devices with touch screen include mobile phones, especially smartphones and tablet computers and PDAs (personal digital assistants). Touch screens can also be found in many other electronic devices, such as in navigation systems, remote controls and door locks.
A large part of electronic devices with a touch screen contains personal data such as emails, passwords and credit card numbers that must be protected against unauthorized access. For this purpose, usually, the input of a password is required when the device is turned on. After correct input of the password a certain action is executed, such as unlocking the device for full use. As an alternative to entering a password, a specific pattern can be required, which is drawn with a finger on the touch screen. As described in patent specification WO 2011/143476 A1, the input of different patterns can also merely result in the execution of actions which do not unlock the device for full use, such as displaying the email mailbox during activated screen lock.
If the device is not used for a certain time, a screen lock usually activates automatically or the device goes into standby mode. For further use of the device after the screen lock or the standby mode was activated, it is required to enter the password again. For devices such as electronic door locks with touch screen the primary function of such devices is to provide protection from unauthorized access. After input of the correct password on a door lock, an action is executed that allows to open the door.
For password input via a touch screen usually a keyboard is displayed on the touch screen on which the letters and/or numbers of the password are successively touched with a finger tip. Since the display of the time is an important feature especially on mobile electronic devices such as smartphones, the current time is displayed in addition to the keyboard often in combination with the date. When the screen lock is activated, therefore, the current time can be read without deactivating the screen lock.
For a comfortable input of the password, the keys of the keyboard which is displayed for entering the password are usually of similar dimension as a fingertip. Already with a keyboard with the numbers 0 to 9, the keyboard occupies about two-thirds of the screen on a smartphone. For the input of the above mentioned pattern a similar amount of space is needed on the screen as well. This has the disadvantage that the remaining space is often not sufficient to display additional information. Such additional information could for example include notifications about the latest calendar events or new messages such as email, SMS or MMS. The display of the time is limited by the display of a keyboard on the screen as well. Here, the remaining space on the screen is not sufficient to display an analog clock in a comfortable size for reading. The time display while displaying a keyboard is therefore mainly based on simple digital clocks.
Another disadvantage of the password input by tapping the alphanumeric characters such as letters or numbers of the password on a keyboard displayed on the touch screen are the traces that are left on the touch screen. These smudges can firstly result from residues on the touch screen or secondly from sweat or grease on the finger. The touch screen can be dirty e.g. from residues of detergent, dust or sweat and grease for example from putting a smartphone to the ear to make phone calls. In this layer the finger or in general the object with which the touch screen is operated then draws the smudges of the password. With a residue free clean touch screen on the other hand, the sweat and grease on the finger are sufficient to leave traces of the password on the touch screen. Such traces will remain on the screen until they are worn away.
Based on the smudges on the touch screen, the alphanumeric characters from the password can be read which makes it considerably easier to decrypt the password and thus gain unauthorized access. The pattern described in patent specification WO 2011/143476 A1, which is drawn with a finger on the touch screen can as well be detected from the smudges left on the touch screen.